Portsmouth's winning run came to an end as they slipped to a 23-17 defeat at Sutton & Epsom in London South One.
The visitors allowed themselves to be disrupted by some old heads in the home pack and paid the price.
'We fell into the trap of letting them rattle us,' said coach Ian Chandler.
'In the first five minutes we were all over them and missed three great scoring opportunities.
'Then, all of a sudden some of their older, experienced forwards started weighing into us.
'It all got a little bit tetchy, we allowed ourselves to get involved and as a result lost focus.
'We gave away a succession of silly penalties and had Ben Whitley yellow carded for dissent.'
The hosts held a 16-3 lead at half-time and Portsmouth brought on outside-half Phil Cartmill and Matt Peters.
It proved a totally different contest after the interval, with Cartmill making an impressive debut.
Tries from Dan Gates and Jason Crabb, both converted by Lee Chandler, got them back into the game but Sutton & Epsom also added a breakaway try.
'We left ourselves with too much to do, although we almost snatched it at the death,' said Chandler, left.
'A try-scoring pass to Dan Sergeant went astray at the end.
'Hopefully it is another lesson learned for our young side, the oldest of whom was 26 years old.
'We are not too down, though, because we played some good rugby.'